The present invention refers to an optical device, more particularly for a reflection detector, comprising an emitter optic for projecting a light beam onto an object and a receptor optic for projecting the reflected light onto a detector.
Reflection detectors require emitter and receptor optics disposed side by side on the front side. Their construction is particularly difficult in the case of compact sensors intended for enclosures having a cross-section of a centimeter or less. Anterior solutions use optical elements molded of synthetic materials which offer very little resistance to aggressive environments and whose surfaces are deteriorated by cleaning. The use of windows or of optical elements of glass complicates the assembly and further reduces the optical aperture and thus the luminous intensity. This is particularly disadvantageous in the case of the mentioned detectors of small dimensions as a limitation of the performance and consequently of the possible applications are the results.
If optical fibers are grouped for producing compact reflection detection systems, the performance of the latter is limited by the angle of aperture. In the case of step-index fibers, which are often used in industrial applications, the angle of aperture is generally close to twice 30xc2x0. The fast light dispersion does not allow to distinguish small objects at a distance of some centimeters.
It is therefore necessary to provide a focusing optic at the ends of these fibers, and no satisfying solution has been found for reflection tips smaller than some millimeters. In fact, optical systems including multiple elements are difficult to integrate into tips having a circular opening. Not even the use of relatively expensive index gradient lenses has provided a simpler solution or led to a significant industrial production.
On the background of this prior art, it is a first object of the present invention to allow the production of an optical device of small dimensions using simple and inexpensive optical elements. A second object is to provide a maximum utilization of a circular opening and thus the highest possible luminous intensity of the optical system, thereby ensuring an optimum performance of the reflection system. A third object is to provide an optical system of a simple construction in order to facilitate its industrial manufacture and to reduce its costs. These objects are attained by an optical device wherein the emitter optic and the receptor optic each comprise a dome disposed in such a manner that the light beam passes through the dome in a plane that is at least approximately parallel to the plane surface of the dome.
In one embodiment, the invention allows to produce a focusing optic disposed at the end of the emitter and receptor fibers and forming a reflection detection tip of some millimeters in diameter.